The NBA has forever been known as a league of giants. In a general sense, that hasn't changed.

The average height for an American male adult is about 5'10", depending on where you look. In the NBA universe, that height is an aberration. According to Basketball-Reference.com, the average height in the league has rounded off at 6'7" in each of the last 32 seasons. Just 25 players 5'10" or under have appeared in a game during that span. What is the percentile rank of the height of a 6'7" American male? Beats me. Every chart I could find cuts off at 6'4", which in itself tells you something. The taller guys represent about the top 2-3 percent of all of us and an unusual, but still miniscule, portion of those people are playing professional basketball.

So, yes, the NBA is a giant's league. But it may be getting smaller.

Clearly the league has become less big-man oriented since the advent of the 3-point line. Just to pick a pre-3 season at random, consider 1988-89. It was 10 years after the advent of the 3-point line yet the inside-out aura of the NBA glimmered unimpeded. That season, players whose primary position was center accounted for 20.8 percent of all minutes and 19.0 percent of all points. Last season, those numbers were 14.3 percent of minutes and 12.8 percent of points.

Those numbers were exceedingly low. The trend over the last 20 years has been towards smaller lineups, but the drift hasn't been linear. In terms of five-year rolling averages, the minutes split between bigs (centers/power forwards) and smalls (everyone else) was 40/60 in 1992-92. Last season, the five-year trend dipped to 36/64 in favor of smalls. It's been as low as 35/65 a few years ago, and there is a lot of year-to-year fluctuation in the averages. The long-term trend has remained clear: We are seeing less-and-less of the traditional center in the NBA.

Like all sports leagues at all levels, the NBA is a copy cat circuit. When the Miami Heat all but abandoned traditional configurations during its run to last season's championship, it heralded a possible new era of positionless lineups. While coaches still value the rim protection and rebounding that old school centers provide, the Heat have shown that defensive versatility and athleticism can compensate without those qualities. Want to protect the rim? Keep teams out of the lane in the first place because if you can, the rewards elsewhere on the court are considerable.

The introduction of the 3-point line for the 1979-80 season heralded this evolution. Before that, coaches at every level of hoops preached the importance of getting the ball inside. With no bonus for long-range shooting, the percentages were simple: The closer you got the ball to the hoop, the more efficient your offense was. This put a premium on post scoring and dribble penetration because not only were the shooting percentages higher on those plays, but the only "extra" points to be found were at the free throw line. At the start, teams made less than one trey per game, so coaches didn't have to adjust their strategy. Now the average team makes more than six 3-pointers per game and to field an efficient defense, you have to chase opponents off the arc.

The shift was furthered by introduction of the NBA's crackdown on hand-checking a few years ago. Suddenly inside-out basketball was just as likely to mean that a quick guard with a good handle was breaking down a defense off the dribble. That aforementioned 6.5 percent drop in minutes per center has been re-distributed in an interesting fashion. Power forwards who now slide over to five are on floor 3.1 percent more often. Small forwards have actually seen their minutes fall by 1.2 percent. The guard positions are up by a combined 4.5 percent. Coaches want to spread the floor with shooters and they want players who can handle the ball.

Of course, positional distinctions are increasingly arbitrary in today's league. We call Kevin Durant a small forward, yet when you watch him stride onto the court there is nothing small about him. LeBron James was also primarily a small forward until Miami's title run. Now he's a power forward on the scoresheet but in reality he's positionless, capable of occupying any space on the floor on any given possession on either end of the floor. What position is a player? That depends on what other players are on the floor and what play the coach has drawn up. Keeping track of it is like eating soup with a fork.

But of course we like to keep track of things, no matter how elusive they might be. So with all these trends noted, we bring you The Big Man Index. Each week, we'll be tracking how big men are used across the league and measuring their production. Using NBAPET, my system for evaluating and tracking the league, we'll monitor the lineups coaches are using on a possession-by-possession basis and ranking the players the "big" positions that we've always called center and power forward, respectively. In any given week, these players may not be "big" at all. Our system will measure the production of players only when they play four or five, which means that James and any other small-ball candidate can slip into the rankings. The rankings will be based on each player's WARP over the previous seven days while playing four or five, and will also incorporate a clutch factor using a basketball version of Win Probability Added.

In addition to ranking the results of the past week, we'll also be projecting the next week going forward, which will be of interest to our fantasy basketball-playing readers. These rankings will forecast weekly production based on quality of opponents and other scheduling factors. Today though, we'll keep it simple since we don't have any real results to work with. Using the SCHOENE projections from Pro Basketball Prospectus 2012-13, we'll rank the top 10 big men going into the season based on each player's base position. This will leave out James and other guys who are small in no other way but in an NBA context, but only for now. Then we'll spotlight three big guys who will be in action during the season's first two nights. The Big Man Index will run each Thursday.

Projectd Top-10 Big Men for 2012-13

1. Dwight Howard, Lakers (15.2 projected WARP): The game's best big man is a traditional center with decidedly non-traditional athletic ability. Now Howard is in new environs and it will be fascinsting to see the effect the Lakers' star-studded cast has on his numbers.

2. Kevin Love, Timberwolves (14.2 projected WARP): In today's NBA, it's vital even in traditional lineups that one of your big men can knock down face-up jumpers. Love of course offers that with an excellent 3-point shot, but offers the killer added value of premier offensives rebounding.

3. Ryan Anderson, Hornets (13.8 projected WARP): Anderson's numbers have been tethered to Howard and because of that, his projection is exaggerated. Still, in many ways Anderson has come to typify what coaches have come to seek in a modern-day four: 3-point shooting and defensively rebounding.

4. Andrew Bynum, 76ers (12.8 projected WARP): The mobility required of current centers is an off-shoot of the preponderance of pick-and-roll basketball and it applies to both ends of the floor. Bynum has that plus a back-to-the-basket skill set that is a throwback. As the featured player in Philly, Bynum will offer the old school brand of inside-out basketball.

5. Blake Griffin, Clippers (12.3 projected WARP): Once upon a time, power forwards were either low-usage, dirty-work players like Marc Iavaroni and Kurt Rambis, or more skilled muscle men like Buck Williams, Truck Robinson and Karl Malone. Now you have Blake Griffin, who jumps like Jordan in his prime and gets down the floor as quickly as any player in the game.

6. Josh Smith, Hawks (11.1 projected WARP): Smith is a hybrid player who can swing between any of the three frontline positions. He's never developed the face-up game that would mark him as a true stretch player, though that's never stopped him from trying. Still, Smith offers a complete set of skills, with rebounding numbers that go up annually and elite weakside shot-blocking.

7. Anthony Davis, Hornets (10.9 projected WARP): We may not have seen an impact defender with more upside on the other end of the floor come into the league since Tim Duncan. We have to remind ourselves that not only is Davis entering what once would have been his sophomore year in college, but he's just three years removed from being a 6'2" guard. Davis is now a power forward on paper, but it will be fascinating to see how his position evolves as Hornets coach Monty Williams learns to fit players around him.

8. Greg Monroe, Pistons (10.7 projected WARP): A center during his first two years, Monroe is being transitioned to the power forward spot. That evolution may be gradual due to the construction of the four-heavy Pistons roster, but the additions of Andre Drummond and Viacheslav Kravtsov portend this shift. With his excellent playmaking skills, Monroe isn't unlike top power forwards of the last two decades like Kevin Garnett and Chris Webber. It's unlikely that he's ever going to be a stretch guy, however, which means that the Pistons are always going to lean on traditional lineups with him around.

9. Kenneth Faried, Nuggets (9.1 projected WARP): Faried is not a floor spacer, but he shows how elite skill sets always find away onto the floor no matter what positional trends might be around the league. His stat line generates a list of comparable players that include a lot of centers, Dwight Howard being one of them. However, he's 6'8" and has the mobility to guard stretch fours while still being one of the top offensive rebounders in the league.

10. LaMarcus Aldridge, Trail Blazers (9.0 projected WARP): Aldridge has developed into one of the top offensive big men in the league, adding both usage and efficiency to his game on an annual basis. His numbers are very similar to those of Chris Bosh, only Aldridge is more efficient. With the Trail Blazers fielding an extremely young, transitional roster this season, it will be interesting to see if Aldridge becomes more of a volume scorer.

Three to Watch

(for October 30-31)

11. Joakim Noah, Bulls (8.9 projected WARP): Centers in the NBA not only use to play more and score more, but they also used to get more assists. Now most pivots rely on others to make plays. There are exceptions of course, and Noah is one of them. His passing skills from the high post have been underutilized with Derrick Rose handling the rock, but Noah may add a few dimes to the ante this season with his star point guard rehabbing. He'll open his season against Sacramento's DeMarcus Cousins, ranked 23rd on our preseason big man list. Cousins may be poised for a breakout season, but he's temperamental and Noah has been known to get under the skin of his opponents.

24. Kevin Garnett, Celtics (5.6 projected WARP): The small-ball trend gets the full spotlight treatment on opening night as Garnett faces 17th-ranked Chris Bosh and the Miami Heat. Both players begin the season as starting centers. For Garnett, it was a move 16 3/4 years in the making and the Celtics took off when he made the shift.

30. Jonas Valanciunas, Raports (4.8 projected WARP): The Raptors have never had a center with close to the upside of Valanciunas, whose name won't ring the bells of many casual NBA fans. Will that change? We'll get the first indications of that on the second night of the season, Toronto takes on the Pacers and their own traditional center in 7'2" Roy Hibbert. Hibbert, ranked 26th among bigs in our preseason forecast, will play his first regular-season game after inking a new max contract over the summer. That deal, as much as anything, shows you that NBA teams still value size. As for Valanciunas, it's unclear how much we'll see of him at the outset as veteran journeyman Aaron Gray may get the starting nod.